l> biology 321 - UBC
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Introduction to Moss Morphology

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Schistidium apocarpum

MORPHOLOGY AND development OF THE MOSSES

Similar to plants, the moss lifecycle is perfect in two unique stages - the gametophyte and also the sporophyte. The term that describes this type of life history is dubbed alternation of heteromorphic generations. In vascular plants the dominant stage the this lifecycle is the diploid generation. In mosses, the dominant stage is the haploid generation (the gametophyte). This method that the green, leafy gametophytic organization is haploid (has only one set of chromosomes).

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Grimmia pulvinata

THE GAMETOPHYTE

The gametophyte refers to all organs and tissues that room a component of the haploid generation. There are two various developmental step of the gametophyte: the protonema, and also the gametophore. The protonema is the an initial part the the moss that creates from the germinating spore. That is filamentous form is remarkably comparable to environment-friendly algae. This photosynthesis colonizer lies flat versus its substrate, making it seem as if the absent or tree it grow on is painted green. The protonema will certainly eventually develop leafy shoots referred to as gametophores.

The gametophores are the most conspicuous part of the moss. Although this shoots it seems ~ to differ from moss come moss, over there are many morphological attributes that are typical to most of the mosses. For instance, many mosses have spirally arranged leaves that are one cell layer special (unistratose).

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Plagiomnium insigne - this snapshot shows the spirally kinds leaves typical to most mosses

Generally many mosses have actually multicellular stems and rhizoids connected with these stems. Of course over there are always exceptions to these norms, yet they are rare.

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Rhizoids in the mosses are multicellular, yet uniseriate (exception: Andreaeidae mosses have biseriate rhizoids). This means that more than one cell is required to make a rhizoid and also that these cells are aligned end to end, forming a filament. Rhizoids normally arise native the cortical cells of the stem, yet can occasionally prosper out that leaves. In mosses, the rhizoids have oblique crosswalls and also are non-photosynthetic. Uneven the root in plants, rhizoids execute not absorb water or nutrient from the substrate; instead, your main function is to connect the plant to that substrate. The is believed rhizoids additionally play a function in water retention and also conduction by capillary action.

tribe in mosses room multicellular and can display a how amazing amount of tissue differentiation depending on the varieties of moss. Typically, many mosses have cortical cells (also called parenchyma cells) that compose much of the stem, and also thick walled cells called stereids for structural support. Part mosses have actually internal conducting strands that overview water and even metabolites with the stem. In general the cells that conduct water are referred to as hydroids and also cells the conduct metabolites are called leptoids. Most hair cap mosses (Polytrichidae) have actually highly differentiated stem cells. Trunk can likewise have appendages various other than leaves. For example, paraphyllia, which room tiny photosynthetic filaments, are discovered on the tribe of a couple of mosses, such together Hylocomium splendens. Some varieties of Sphagnum have retort cell (elongate cells v a pore end the upper end) associated with the surface of the stem

The pipeline are really interesting organs due to the fact that they can show a an excellent degree the specialization between different varieties of moss. Generally, most leaves room photosynthetic and are composed of a solitary layer the elongate cells. Uneven the pipeline in irpari liverworts, mosses have actually leaves that room spirally arranged and are never lobed (although this can be disputed when considering the pipeline of Takakia). Plenty of moss leaves also have a costa, i beg your pardon is a midrib of devoted cells that runs lengthwise through the leaf.

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Atrichum leaf showing devoted cells

Like the stem, the cell of the costa can show a great deal of differentiation. These specialized cells include: stereids, guide cells, hydroids and also leptoids. Guide cells are noticeable big cells that room continuos v the cells that make up the rest of the sheet blade (the lamina). Leaves have the right to have many modifications that are particular to family, or to a species, and also are really useful as soon as trying to determine a moss. Right here is a perform of few of these novel characteristics:

Undulations: refers to waves that operation perpendicular to the length of the sheet
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Snake moss reflecting undulating leaves
Pleats: refers to wrinkles that run along the length of the sheet toothed margins: space sharp extensions of the leaf margins - check out Atrichum picture above lamellae: photosynthetic cell that kind filaments or plates follow me the lamina or costa that the leaf. Lock are found in the Polytrichidae incurved margins: spare that space curved upwards and towards the facility of sheet recurved margins: margins that room curved downwards and towards the center of the sheet hair suggest / awn: describes the extension of the costa past the guideline of blade, producing a hair or bristle.
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Grimmia pulvinata - sheet awn
Papillae: describes bulges that cell wall thickenings of certain cells Pits: refers to a perforation or hole in the cell wall surface of details cells. Hyaline cells: Large, non-photosynthetic, porous cells discovered in Sphagnum leaves.
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SEM the Sphagnum rubellum hyaline cells
Alar: refers to the basal edge of a leaf whereby cells space most often larger 보다 the other cells the the leaf.

The archegonia and also the antheridia space the female and also male reproductive offal in the mosses. The masculine will develop coiled biflagellated sperm cells that will certainly swim in the direction of the egg that lies in ~ the archegonia. Due to the fact that water is essential for the sperm cells to reach the egg, this is among the factors why moss seem come be more prevalent in wet areas. When fertilized, the zygote will certainly mature to develop the sporophyte.

THE SPOROPHYTE

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Atrichum undulatum sporophyte Polytrichum piliferum sporophyte

The sporophyte refers to the diploid generation the the moss. It stays attached to the gametophyte (the haploid mother), and also is in fact, helminth upon it. The sporophyte counts on the gametophyte to administer it with food and water, which room passed through transfer cells that lie in the placental layer in between the gametophyte and also the sporophyte. Deliver cells have actually convoluted cell wall surfaces that rise surface area because that nutrient exchange. In many mosses the sporophyte will have actually these anatomical features: a foot, seta, a sporangium v a columella, spores, one operculum, peristome teeth, and a calyptra.

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Atrichum undulatum teeth - sporangium cross section Peristome teeth of a bryidae member - microscopic view
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Bartramiopsis lescurii - tooth-less sporangium Dawsonia superba sporophyte - keep in mind myriad bristle-like teeth

Most moss sporophytes have a seta except for those in the Andreaeidae and also the Sphagnidae, which have actually pseudopodia instead. A seta is a lengthy stem-like body organ that associate the sporangium come the gametophyte. In mosses the seta elongates before the sporangium matures, i m sorry is opposite to the liverworts. The seta is normally composed that parenchyma cells, stereids, and also many times a well occurred conducting strand. Many varieties of moss have actually both hydroids and leptoids in the seta. The base of the seta is referred to as the foot.

The sporangium is the key body of the sporophyte and also is the organ in which the spores room produced. As formerly mentioned, most mosses will have actually a sporangium through these anatomical features:

A sporogenous layer, a columella, peristome teeth, and also an operculum.

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Also, many mosses (except Sphagnum) have a calyptra to safeguard the developing sporangium. This calyptra is technically gametophytic, because it is created of haploid tissue that was once a part of the archegonium. The calyptra have the right to take many different forms depending on the species of moss. It deserve to be outright (most mosses) or hairy (mosses in the Polytrichidae). This appendage will eventually be burned prior to spore dispersal.

Polytrichum piliferum - showing its hairy calyptra

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